MODELING OF FULL AND LIMITED IRRIGATION SCENARIOS FOR CORN IN A SEMIARID ENVIRONMENT K. C. DeJonge, A. A. Andales, J. C. Ascough II, N. C. Hansen ABSTRACT. Population growth in urbanizing areas such as the Front Range of Colorado has led to increased pressure to transfer water from agriculture to municipalities. In some cases, farmers may remain agriculturally productive while practicing limited or deficit irrigation, where substantial yields may be obtained with reduced water applications during non‐water‐sensitive growth stages, and crop evapotranspiration (ET) savings could then be leased by municipalities or other entities as desired. Site‐specific crop simulation models have the potential to accurately predict yield and ET trends resulting from differences in irrigation management. The objective of this study was to statistically determine the ability of the CERES‐Maize model to accurately differentiate between full and limited irrigation treatments in northeastern Colorado in terms of evapotranspiration (ET), crop growth, yield, water use efficiency (WUE), and irrigation use efficiency (IUE). Field experiments with corn were performed near Fort Collins, Colorado, from 2006 to 2008, where four replicates each of full (100% of ET requirement for an entire season) and limited (100% of ET during reproductive stage only) irrigation treatments were evaluated. Observations of soil profile water content, leaf area index, leaf number, and grain yield were used to calibrate (2007) and evaluate (2006 and 2008) the model. Additionally, ET and water use efficiency (WUE) were calculated from a field water balance and compared to model estimates. Over the three years evaluated, CERES‐Maize agreed with observed trends in anthesis date, seasonal cumulative ET (Nash‐Sutcliffe efficiency ENS = 0.966 for full irrigation and 0.835 for limited irrigation), leaf number in 2007 (ENS = 0.949 for full irrigation and 0.900 for limited irrigation), leaf area index in 2008 (ENSĂ= 0.896 for full irrigation and 0.666 for limited irrigation), and yield (relative error RE = 4.1% for full irrigation and ‐3.4% for limited irrigation). Simulation of late‐season leaf area index in limited irrigation was underestimated, indicating model overestimation of water stress. Simulated cumulative ET trends were similar to observed values, although CERES‐Maize showed some tendency to underpredict for full irrigation (RE = ‐7.2% over all years) and overpredict for limited irrigation (RE = 12.7% over all years). Limited irrigation observations showed a significant increase in WUE over full irrigation in two of the three years; however, the model was unable to replicate these results due to underestimation of ET differences between treatments. While CERES‐Maize generally agreed with observed trends for full and limited irrigation scenarios, simulation results show that the model could benefit from a more robust water stress algorithm that can accurately reproduce plant responses such as those observed in this study. Keywords. CERES‐Maize, Crop modeling, Deficit irrigation, Evapotranspiration, Limited irrigation. n several areas of the U.S., including the Front Range rado is expected to increase by 65% from 2000 to 2030 of Colorado, large urban population growth is occurring (CDM, 2007). To deal with large municipal growth, cities despite limited availability of water resources. Agricul‐ have purchased water rights from farmers. In many cases, this tural uses currently account for more than 85% of the to‐ transfer involves all water rights and often the land, leading talI water consumed in Colorado, and agricultural users hold to dry‐up of large areas and adverse ecological and socio‐ most of the senior water rights (CDM, 2007). Furthermore, economic consequences for rural communities (Colorado population in the South Platte River basin of northeast Colo‐ Water, 2010). CDM (2007) predicts that nearly 37% of the ir‐ rigated area in the South Platte River basin (54,000 ha) will be lost between 2000 and 2030. In addition to potential eco‐ nomic losses to farmers and smaller communities that depend Submitted for review in June 2010 as manuscript number SW 8617; on agriculture, this loss could cause negative environmental approved for publication by the Soil & Water Division of ASABE in impacts from leaving land fallow, such as erosion by wind, January 2011. Presented at the 2010 ASABE Annual Meeting as Paper No. 108897. weed invasion, lack of management (Skidmore et al., 1979), The authors are Kendall C. DeJonge, ASABE Member Engineer, and soil carbon loss (Paustian et al., 1997). Current Colorado Graduate Research Assistant, Department of Civil and Environmental water law is based on the prior appropriation system of water Engineering, and Allan A. Andales, ASABE Member Engineer, Assistant allocation, the main components of which place high empha‐ Professor, Department of Soil and Crop Sciences, Colorado State University, Fort Collins, Colorado; James C. Ascough II, Research sis on return flow conservation and quantification of con‐ Hydraulic Engineer, USDA‐ARS Agricultural Systems Research Unit, Fort sumptive use or evapotranspiration (ET) (Colorado Water, Collins, Colorado; and Neil C. Hansen, Associate Professor, Department 2010; Smith et al., 1996). Current water rights transfers allow of Soil and Crop Sciences, Colorado State University, Fort Collins, only for complete transfer of consumptive use, but some re‐ Colorado. Corresponding author: Kendall C. DeJonge, Department of searchers note that changes in water law are likely as irriga‐ Civil and Environmental Engineering, Colorado State University, Campus Delivery 1372, Fort Collins, CO 80523‐1372; phone: 970‐491‐1141; fax: tors find increased pressure to use their water more 970‐491‐0564; e‐mail: kendall.dejonge@colostate. edu. economically (Smith et al., 1996; English et al., 2002). En‐ Transactions of the ASABE Vol. 54(2): 481-492 2011 American Society of Agricultural and Biological Engineers ISSN 2151-0032 481 glish et al. (2002) suggest that a fundamental change is neces‐ ple, Xie et al. (2001) found that simulated vegetative growth sary in the way that producers approach irrigation and kernel weight were extremely sensitive to growth stress. management. They propose that irrigated agriculture adopt Additionally, López‐Cedrón et al. (2008) evaluated CERES‐ a new paradigm based on the maximization of net benefits, Maize for rainfed and irrigated treatments with the intent to instead of simply the biological objective of maximizing improve model ability in predicting biomass and yield under yields. water‐limited conditions. They found that the model ade‐ One example of this proposed change is limited irrigation quately predicted yield from irrigated treatments but under‐ of crops. Limited irrigation practices incorporate water man‐ predicted yield from rainfed treatments. Other researchers agement under restricted water application and minimize wa‐ have found that CERES‐Maize overestimated the effects of ter stress during critical crop growth stages in order to water stress on vegetative growth and subsequently adjusted maximize yields (Schneekloth et al., 2009). Older field stud‐ the stress functions and improved simulation results (Nouna ies have addressed maize response to growth‐timing of irriga‐ et al., 2000; Mastrorilli et al., 2003). Recent studies have em‐ tion (e.g., Barrett and Skogerboe, 1978; Doorenbos and phasized management of crops under stressed conditions, Kassam, 1979; Gilley et al., 1980). More recent studies have with some researchers suggesting a need for increased under‐ supported this idea, e.g., Klocke et al. (2004) achieved 93% standing and development of accurate simulations of water of fully irrigated corn yield using 76% of the water applied. stress on various growth and development processes In a separate study, Klocke et al. (2007) achieved limited ir‐ (e.g.,ĂSaseendran et al., 2008b). Limited water resources and rigation yields of 80% to 90% of fully irrigated yields while increasing pumping costs have caused farmers in Colorado to using about half the applied water compared to full irrigation. consider limited irrigation as an alternative to full irrigation More recent studies regarding the importance of growth‐ practices. Alternatively, farmers may consider either a reduc‐ stage directed irrigation timing include Payero et al. (2006), tion in planted area or schedule irrigation events so that plants Igbadun et al. (2008), Farre and Faci (2009), Ko and Piccinni do not encounter stress during sensitive growth stages. For (2009), Payero et al. (2009), and Mansouri‐Far et al. (2010). example, Saseendran et al. (2008a) simulated various water Accurate crop simulation models, such as those found in allocations and irrigation amounts in northeastern Colorado the Decision Support System for Agrotechnology Transfer using CERES‐Maize and found that split irrigation applica‐ (DSSAT v4.0), can play a role in assessing the costs and bene‐ tions of 20% of the total water applied during vegetative fits of limited irrigation and the interactions of timing and growth stages and 80% of the total water applied during re‐ amount of irrigation (Hoogenboom et al., 2004). The DSSAT productive growth stages obtained the highest yield for a giv‐ Cropping System Model (CSM)‐CERES‐Maize model en irrigation allocation (ranging from 100 to 700 mm of total (Jones and Kiniry, 1986; Ritchie et al., 1998; Jones et al., irrigation). 2003) has been widely used to assess cropping and manage‐ Additional research